Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
  • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
  • G06V40/16—Human faces, e.g. facial parts, sketches or expressions
  • G06V40/172—Classification, e.g. identification
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F18/00—Pattern recognition
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T1/00—General purpose image data processing

Definitions

• the invention relates to a biometrical identification device.
• the invention also relates to a method being implemented by such a device.
• the invention is particularly relevant in the domain of access control based on biometry.
• biometrical identification When a biometrical verification is to occur, a scan of the fingerprint of a person is made and compared with stored characteristics of a reference fingerprint.
• a first problem when using biometrical identification based on the basis of fingerprints is the fact that none of the finge ⁇ rint scanners that are currently available can distinguish between a finger and a well-created dummy.
• a second problem is that such biometrical identification systems have non-zero false accept and false reject rates. Sweat pores are naturally occurring physical characteristics of the skin, which exist upon the ridges of the fingerprint and provide additional patterns for biometrical identification.
• Patent Application published under number WO99/06942 discloses a method of and a device for identifying individuals from association of finger sweat pores and macro- features.
• the method comprises obtaining from an individual during a registration process, a fingerprint image having at least one registration pore and at least one registration macro- feature.
• Registration pore data is derived from the registration pores and registration macrofeature data is derived from the registration macrofeatures.
• a bid step a fingerprint image having at least one bid pore and at least one bid macrofeature is obtained.
• Bid pore data is derived from the bid pores and bid macrofeature data is derived from the bid macro- features.
• Bid associated data is constructed from associating the bid pore data with the bid macrofeature data, and constructing registration associated data derived from associating the registration pore data with the registration macrofeature data.
• the bid associated data is compared to the registration associated data to produce a correlation score where a successful or failed identification result is produced based on comparison of the correlation score to a predetermined threshold.
• Such a method enables a substantial reduction of the false accept and false reject rates by associating macrofeatures and sweat pores. Moreover the method has improved fraud fighting capabilities, because sweat pore information is harder to retain on impostor fingerprints. Finge ⁇ rint duplication with cooperation is compulsory.
• a first drawback of this method is that the presence of dirt and oil on the finger surface perturbates the detection of sweat pores. The obtained sweat pore data is therefore not very reliable and cannot be exploited as a unique source of identification data.
• a second drawback is that, although fraud is made more difficult, it is still possible.
• the object of the invention is to provide a solution for identifying an individual, which is more reliable and more resistant to fraud.
• a biometrical identification device comprising: - acquisition means for acquiring an intra-skin image, said intra-skin image being located inside the fmger at a distance from the inside surface of the fmger, said intra-skin image comprising sweat pores,
• - location means for locating candidate sweat pores as isolated spots in said intra-skin image
• - matching means for matching said candidate sweat pore locations with reference pore locations of a reference intra-skin image to produce a pore matching score
• the acquisition means in accordance with the invention provide an intra-skin image of the individual fmger. Said image is located inside the individual finger at a certain distance of the finger surface.
• An advantage of acquiring such an intra-skin image is to get rid of any pollution of the physical characteristics of the skin by external factors like dirt and oil. Image quality and visibility of physical characteristics are greatly improved.
• Such an intra-skin image not only shows the classical pattern of ridges and valleys of a conventional finge ⁇ rint, but also the sweat pores with an enhanced visibility.
• the pore locating means exploit this enhanced visibility for locating candidate sweat pores either as isolated bright spots on a dark background or as isolated dark spots on a bright background.
• the candidate sweat pore locations are matched with reference sweat pore locations in order to produce a pore matching score. If said pore matching score is greater than a predetermined pore threshold, the individual finger is considered as the actual one. If not, it is considered as an impostor. Sweat pores are known to those skilled in the art as permanent, immutable and individual characteristics.
• the biometrical identification device in accordance with the invention therefore provides a very reliable identification of an individual finger, which is only based on said sweat pores.
• fraud is made very difficult by the biometrical identification device in accordance with the invention, because acquiring an intra-skin image located at a certain distance inside the individual finger is not as simple to implement as acquiring a superficial image of the finge ⁇ rint.
• - Fig. la shows a conventional finge ⁇ rint
• Fig. lb shows a zoom on an intra-skin image in accordance with the invention
• - Fig. 2 shows a flow chart diagram of a biometrical identification device in accordance with a first embodiment of the invention
• - Fig. 3 is a schematic diagram of the acquisition means in accordance with the invention
• Fig. 4 shows a flow chart diagram of a biometrical identification device in accordance with a second embodiment of the invention
• - Fig. 5a shows a schematic view of an intra-skin image comprising ridges, finge ⁇ rint macrofeatures and sweat pores
• - Fig. 5b shows a schematic view of a search area of sweat pores around a macrofeature location within the intra-skin image
• - Fig. 6 is a schematic diagram of the biometrical identification device in accordance with a third embodiment of the invention
• - Fig. 7a and 7b show a searching area centered on a macrofeature of a finge ⁇ rint ridge for searching sweat pores in accordance with a second embodiment of the invention
• FIG. 8 is a schematic diagram of the biometrical identification device in accordance with a fourth embodiment of the invention.
• an inside surface 2 of an individual finger 1 is pressed on a plate 3 of acquisition means 4.
• Said acquisition means 4 are intended to acquire an intra-skin image ISI of an image plane IP of the finger 1, said image plane IP being located inside the finger 1 at a distance D from the inside surface 2.
• Said distance D from the inside surface 2 of the finger is advantageously chosen greater than 0.1 and less than 0.5 mm.
• the acquisition means 4 presented in Fig. 3 comprise a radiation source 41 for generating a radiation beam 42, such as, for instance, a laser beam.
• the acquisition means 4 further comprise focusing means 43, for instance an objective lens, for focusing the radiation beam 42 on the image plane IP inside the finger 1.
• the acquisition means 4 finally comprise detection means 44 for detecting a reflected radiation beam, said reflection beam 45 being reflected from the image plane IP.
• the acquisition means 4 comprise a confocal microscope, which form an image from an emitted laser light, but it will be apparent to a person skilled in the art that the invention also concerns any equivalent system capable of producing such an image ISI of the image plane IP, for instance a medical X ray system.
• Fig. 4 describes in a schematic way how the intra-skin image ISI is formed by the acquisition means when a confocal microscope is used.
• a confocal microscope comprises: - a laser source 10 which provides an excitation light 11,
• dichro ⁇ c mirror 12 which reflects light shorter than a certain wavelength and passes light longer than that wavelength
• a collimator lens 15 which makes laser rays parallel
• an objective lens 16 having a focal point F, which is located in the image plane IP into the skin of the finger 1 (the objective lens 16 has a focal plane which is identical to the image plane IP)
• the laser source 10 produces the excitation light 11, which reflects off the dichro ⁇ c mirror 12. From there the excitation light 11 hits the two scanning mirrors 13 and 14, which scan the excitation light 11 across the finger 1.
• the finger 1 reemits some reemitted light 20, which is descanned by the scanning mirrors 14 and 13, passes through the dichro ⁇ c mirror 12 and is focused onto the confocal pinhole 17. Since the focal plane of the objective lens 16 is conjugate to the pinhole plane, only the light reflected by the finger at the focal point passes the pinhole.
• the reflected light 20 that passes through the confocal pinhole 17 is measured by the detector 18, for instance a photomultiplier tube.
• Fig. lb shows a zoom on an area of an intra-skin image ISI produced by a device in accordance with the invention.
• Said zooming area comprises bright ridges BR and dark valleys DV, which look rather similar to those of Fig. la, but with an inverted contrast.
• the bright ridges of Fig. lb correspond to furrows of the fmger surface and the dark valleys of Fig. lb to the ridges of the finger surface.
• Said intra-skin image ISI comprises in addition to the classical ink-based finge ⁇ rint of Fig.
• the acquisition means could as well provide an intra-skin image with an inverted contrast, that is with isolated dark spots on a bright background. It should be noted that the intra-skin image ISI roughly comprises 10 pores /mm 2 .
• the device in accordance with the invention further comprises location means 5 for locating said isolated bright spots in the intra-skin image ISI.
• said location means 5 are intended to locate candidate sweat pores independently from any other feature of the finge ⁇ rint like for instance finge ⁇ rint macrofeatures.
• the location means 5 for instance implement a thresholding technique in order to extract the candidate sweat pores from the darker background.
• a thresholding technique keeps the pixels of the image ISI, which are greater than a predetermined contrast threshold, while forcing to zero the pixels whose values are less than said predetermined contrast threshold.
• Such a technique well known to a person skilled in the art, leads to a binarization. A binary image is produced.
• the locating means 5 may also comprise filtering sub-means based for instance on a circular filter, which detects bright circular shapes having a contrast value and a diameter included into predetermined ranges of values.
• said location means 5 further comprise thinning sub-means in order to get candidate sweat pores of one pixel width. Thinning techniques used by the thinning sub- means are well known to a person skilled in the art.
• the location means 5 output a set of candidate sweat pore locations CP ⁇ (x ⁇ ,y ⁇ ), CP 2 (x 2 ,y 2 ), ... , CP N (x n ,yn), where n is an integer.
• Matching means 6 then match said candidate sweat pore locations CP ⁇ to CPN with reference pore locations RPi to RP M , where M is an integer, of a reference intra-skin image RI.
• a pore matching score PMS is produced in the following way: said pore matching score PMS is initialized to zero. If a reference pore RP is found within the search area S A, the pore matching score PA is incremented by 1.
• Decision means 7 further compare the pore matching score PMS with a predetermined pore threshold so as to decide whether the identification based on the intra-skin image ISI is valid or not.
• a predetermined pore threshold has a value, which is empirically chosen, in order to eliminate impostor fingers but not true fingers.
• the intra-skin image ISI and the reference image RI may have been acquired with different settings like for instance a different orientation of the individual finger, as shown in Fig. 5.
• An advantage of the first embodiment of the invention is to propose a solution for identifying an individual finger from analyzing only the candidate sweat pores contained in the intra-skin image.
• An advantage of acquiring such an intra-skin image is to get rid of perturbations due to dirt, oil and any degradation of the skin surface. Consequently, the obtained intra-skin image is of good quality and presents well-contrasted sweat pores.
• Another advantage is that no trace of the intra skin pattern can be found on cups or tables.
• the image processing techniques involved for locating and matching the sweat pores also have the advantage to be simple to implement.
• the intra-skin image ISI not only comprises sweat pores but also finge ⁇ rint ridges and valleys.
• Said finge ⁇ rint ridges are usually characterized by macrofeatures, which are well known to a person skilled in the art.
• macrofeatures are for instance bifurcations BF and end points EP of the finge ⁇ rint ridges.
• Fig. 6 presents in a functional way the biometrical identification device in accordance with a second embodiment of the invention.
• Said device further comprises macrofeature location means 30 for locating macrofeatures of said finge ⁇ rint ridges.
• Said macrofeature location means 30 for instance comprise thresholding sub-means for binarizing the intra-skin image ISI.
• a binary intra-skin image BISI is obtained.
• aid thresholding sub-means involve the same kind of technique as the one used by the pore locations means 5. Consequently, the thresholding sub-means can advantageously be applied once to the intra-skin image ISI and the same binary image BISI be used by both pore location means 5 and macrofeature location means 30. In this case, the binary intra-skin image BISI is sent to the pore location means 5. It should be noted that contrast irregularities of the ridges and valleys may induce some errors when thresholding the intra-skin image.
• the macrofeature location means 30 further comprise thinning sub-means in order to produce one-pixel wide finge ⁇ rint structures.
• a ridge skeleton graph or a valley skeleton graph can be output. Both can be used to locate macrofeatures, but it turns out that sweat pores are more easily extracted from the ridge skeleton graph, because sweat pores are located in the valleys.
• the macrofeature location means 30 further comprise analysis sub-means which consist in analyzing each vertex of a ridge in order to determine whether it is a macrofeature (bifurcation or end point) or not. Such an analysis is performed in a searching area, and is in particular based on length criteria. For instance, too short ridges are rejected.
• the macrofeature location sub-means finally output locations of the extracted macrofeatures MFi to MF , where L is an integer.
• Fig. 7a is a schematic view of the binary intra-skin image BISI. Said binary intra-skin image BISI comprises the macrofeature locations MFi to MF L .
• the device in accordance with a second embodiment of the invention further comprises macro-feature matching means 31 for matching said macro-feature locations MFi to MF with reference macrofeature locations RMFi to RMF K , where K is an integer, to produce a macro-feature matching score MFMS.
• the reference macrofeature locations RMFi to RMF K come from the reference image RI and are stored in a memory of the biometrical identification device in accordance with the invention.
• Said macrofeature matching score MFMS is compared with a predetermined macrofeature threshold MFT by macrofeature decision means 32, which output a macrofeature based decision MFD.
• the macrofeature based decision MFD considers the identification of the individual finger based on macrofeatures as valid, if not the identification is considered as failed.
• the macrofeature locations MFi to MF L are advantageously exploited by the pore location means 5 in the following way: instead of searching for pores in the whole intra-skin image ISI, which may be rather time consuming, searching areas SA are delimitated around the macrofeature locations MFi to MF L . In other words, said macrofeature locations MFi to
• Fig. 7b is a schematic view of a searching area SA centered around the macrofeature location MFi for locating sweat pores in the intra-skin image ISI.
• a sweat pore SPi is located at a distance p ⁇ from the macrofeature location MF ⁇ Said sweat pore SPi can be advantageously located with respect to the macrofeature location MF ⁇ using polar coordinates (p ⁇ , ⁇ ).
• the macrofeature based decision MFD is advantageously exploited by the pore decision means 7 in order to take the pore-based decision PD.
• a failed identification of macrofeatures could be considered as prevailing over a valid identification of pores, because the macrofeatures are more specific and easier to identify with certainty than the punctual sweat pores.
• a valid identification of macrofeatures needs to be completed by a valid identification of pores in order to get a more secure decision.
• An advantage of the second embodiment of the invention is to exploit the fact that the finge ⁇ rint macrofeatures are easy to detect in order to make the location of sweat pores more robust to errors. Macrofeature locations facilitate a mapping of the intra-skin image ISI with the reference image RI.
• the biometrical identification device in accordance with the invention produces a sequence of intra-skin images.
• Said sequence of intra-skin images forms a three dimensional intra-skin image, in which each intra-skin image corresponds to a particular depth within the skin of the finger.
• the location means 5 and matching means 6 are applied to each intra-skin image of the sequence, preferably sequentially so as to take the pore locations of a previous image into account for searching for the sweat pores in a current intra-skin image.
• the decision means 7 collect the sweat pore locations coming from the successive intra-skin images of the sequence. Possibly, said decision means assign a reliability measure to the sweat pore locations, depending on a continuity of presence of the sweat pore all along the sequence and takes the final pore based decision on the basis of such a reliability measure.
• a biometrical identification device in accordance with a fourth embodiment of the invention comprises second acquisition means 50 for acquiring a superficial finge ⁇ rint image SI of the inside surface 2 of the finger 1.
• Said second acquisition means 50 for instance comprise a CCD camera.
• the superficial image SI comprises finge ⁇ rint ridges and valleys and pores.
• the main difference with the intra-skin image ISI is that the superficial image SI is noisier, which is due to on the presence of oil and dirt on the finger surface.
• the biometrical device in accordance with the fourth embodiment of the invention further comprises second macrofeature location means 51 for locating macrofeatures located on the finge ⁇ rint ridges of the superficial image SI. Second macrofeature locations RMF'i to RMF' L , where L is an integer, are output
• the biometrical device in accordance with the fourth embodiment of the invention further comprises second macrofeature matching means 52 for matching said second macrofeature locations with second reference macrofeature locations RMF'i to RMF' K , where K is an integer, of a reference superficial image RSI, so as to produce a superficial macrofeature matching score (SMFMS).
• the image processing techniques involved are very similar to those involved in the macrofeature location means 30 and the macrofeature matching means 31 and are well-known to a person skilled in the art.
• the biometrical device in accordance with the fourth embodiment of the invention further comprises second pore location means 53 for locating the sweat pores as isolated bright spots in said superficial image (SI) with respect to the second macrofeature locations MF' t to MF' L . For instance, the sweat pores are searched in a searching area centered around a second macrofeature location. Second sweat pore locations CP to CP'N, where N is an integer are output.
• the biometrical device in accordance with the fourth embodiment of the invention further comprises second pore matching means 54 for matching said pore locations CP' i to CP' N with second reference pore locations RP' i to RP' M , where M is an integer, of said reference superficial image (RSI), so as to produce a superficial pore matching score (SPMS).
• RSI reference superficial image
• the techniques involved in the second pore location means 53 and in the second pore matching means 54 are enhancement, thresholding, thinning and matching techniques, which are well known to a person skilled in the art. However, the presence of noise makes the detection of macrofeatures and pores more difficult. To circumvent this issue, denoising techniques, well known to a person skilled in the art may advantageously be used.
• a superficial pore matching score SPMS is output. The superficial macrofeature matching score SMFMS and the superficial pore matching score SPMS are exploited by second macrofeature decisions means 55 and second pore decision means 56, respectively.
• said second macrofeature decisions means 55 and second pore decision means 56 compare the superficial macrofeature matching score SMFMS and the superficial pore matching score SPMS with predetermined macrofeature and pore thresholds, respectively.
• a superficial macrofeature based decision SMFBD and a superficial pore based decision SPBD are taken.
• the biometrical identification device in accordance with the fourth embodiment of the invention finally comprises global decision means 57 for deciding whether the identification ID of the individual finger 1 is valid or not. Such a global decision is taken using the macrofeature matching score MFMS, the pore matching score PMS, the superficial macrofeature matching score SMFMS and the superficial pore matching score SPMS.
• a first advantage of the system in accordance with a fourth embodiment of the invention is provide a more secure identification, which is obtained from two different image acquisition modes of the finge ⁇ rint.
• a second advantage is to make fraud even more difficult.
• the biometrical identification system in accordance with the invention is particularly useful for access control in a building entrance.
• a system can also be used for mobile identity control, for instance by the police.
• the intra-skin image ISI may be produced by a portable device, which is separated from the biometrical identification system. Therefore, a device for producing an intra-skin image ISI of an individual finger 1 in accordance with the invention comprises placement means for placing an inside surface 2 of the individual finger 1 in front of acquisition means. Said acquisition means further acquire the intra-skin image, which is located inside the finger at a distance (D) from the inside surface (2) of the finger.
• the intra-skin image ISI is finally stored by storage means into a memory.
• the intra-skin image ISI may then be transmitted to the locating means, matching means and decision means of the biometrical identification device in accordance with the invention for instance via a network connection. It should be noted that the transmission may advantageously be encrypted.
• the biometrical identification device in accordance with the invention implements a method for identifying an individual fmger.
• Said method comprises a step of acquiring at least an intra-skin image (ISI) of the individual finger, said intra-skin image being located at a distance inside the finger and comprising sweat pores.
• ISI intra-skin image
• the method in accordance with the invention further comprises a step of locating the sweat pores as isolated bright spots in said intra-skin focused image ISI, a step of matching the pore locations CPi to CP N with reference pore locations RPi to RP M of a reference intra-skin focused image to produce a pore matching score PMS and finally a step of deciding of a successful or failed pore-based identification (PI) from a comparison of the pore correlation score (PCS) with a first predetermined threshold.
• PI pore correlation score

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• 2004
  • 2004-08-24 DE DE602004010825T patent/DE602004010825T2/de not_active Expired - Fee Related
  • 2004-08-24 JP JP2006524453A patent/JP2007504524A/ja not_active Withdrawn
  • 2004-08-24 EP EP04769167A patent/EP1661058B1/en not_active Not-in-force
  • 2004-08-24 KR KR1020067004027A patent/KR20060123710A/ko not_active Application Discontinuation
  • 2004-08-24 AT AT04769167T patent/ATE381739T1/de not_active IP Right Cessation
  • 2004-08-24 US US10/569,017 patent/US20070003114A1/en not_active Abandoned
  • 2004-08-24 CN CNA200480024441XA patent/CN1842805A/zh active Pending
  • 2004-08-24 WO PCT/IB2004/002740 patent/WO2005022446A1/en active IP Right Grant

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